In internal combustion engines of this kind, there are frequently minor variations in the relative positioning of the engine body or crankcase and the shell due to manufacturing tolerances and/or differing weights of the shell or the assembly carried thereby (fuel tank, oil cooler or the like). Moreover the intrinsic vibration frequency or characteristic of the shell and, therefore, the sound dissemination thereof is influenced by various factors (engine speed, inertial forces and the like).
It is an object of the present invention to provide means to enable variations of position between the engine body or crankcase and the shell to be compensated for and the intrinsic vibrations of the shell corrected. In accordance with the invention, at least one spring arrangement is provided between the engine body or crankcase and the shell detachably connected thereto by suspension elements, in which arrangement at least one spring means is provided between the engine body or crankcase and the shell preferably at a lower part of the engine, said arrangement being adjustable in effect by an adjusting device.
Where use is made of springs of constant pitch, the axial lengths of the springs can be varied by means of the adjusting member while still retaining the spring constants and thus any variation in position eliminated. Where use is made of springs of progressive pitch, not only can intrinsic vibration of the shell be corrected but also, for example by inserting washers, variations in position between the parts can additionally be compensated.